1. Go ultra-minimalist when building, never enable memories, and don't travel. The more objects placed on the lot or kept in inventory the more opportunities for one of them to get corrupted (not to mention they all increase the overall file size). As many of us just experienced in the recent memory challenge enabling memories causes file bloating and lots of bugs. And travelling is always dangerous with potential glitches, plus each world travelled to creates its own cache within your save file, increasing the overall save size.
2. Don't let the mother listen to kids music or watch kid's television. Everything else to increase multiples is something you'd have to direct them to do (procreation elixirs, wishing for large families, fertility treatment reward, etc). But if her favourite music is kids or she's childish and has access to a radio and television - watch out!
...and Rica the ninja strikes from the shadows to answer with surgical precision. Basically, what she said.
Edit: Oh, just remembered an oldie but goodie. If you aren't already in the habit, I recommend never using the "Save" option but always using "Save As." Having rolling saves is even better (save1, save2, save3, etc). I don't know if it's still necessary now, but back in the day using 'Save As' was the only way I could prevent file corruption and the loss of save files.
